Know the rules first: how to play.

Ditch high cards early

A lone king is 10 points of risk if someone goes out on you. Middle cards (6-9) have more run neighbors, so hold them a turn or two longer.

Don't feed your opponent

Every discard tells them something. Took a 7♦? Probably building around 7s or diamonds, so don't hand them the 6♦ or 8♦. Discard what they've shown no interest in.

Stock over discard pile

Take from the discard pile only when it completes a meld you're close to. Anything else just reveals your hand. Stock draws keep you hidden.

Knock or push for gin?

• Knock low, knock safe. Lower deadwood = safer knock. Opponent beats you after layoffs and you eat an undercut.
• Push for gin when close. Denies layoffs, adds 20 points. Worth the extra turn if you're in single digits.

Rule of thumb: knock as soon as it's safe late in a hand; hold out for gin earlier when you've got turns to spare.

Watch the stock count

Low stock = lower value in waiting for a better draw. A hand that goes to the wall scores nobody anything.

Practice

Play a match and discard with their pickups in mind, not just your own hand. See also: how the ladder and the bot's difficulty work.